1. Field of the Invention
The present invention relates to the improvement of a braking system.
2. Background of the Invention
A hydraulic braking device is popularly used in a vehicle such as a motorcycle. There has been known a hydraulic braking device in which a braking input side where a liquid pressure is generated when a rider operates a braking operation part and a braking output side where the liquid pressure is supplied to wheel braking means. The braking input side and the braking output side are communicated with each other or interrupted from each other due to an operation of a solenoid-operated open/close valve.
As an example of such a hydraulic braking device, there has been known a so-called by-wire-type braking system which electrically detects a control variable of the braking operation part, controls a liquid-pressure generation device based on the detection value so as to generate liquid pressure, and operates a wheel braking means.
In such a by-wire-type braking system, to enable braking corresponding to the braking operation, a pressure sensor is provided to a braking input side. To perform a malfunction diagnosis of the pressure sensor, output values of a plurality of pressure sensors are compared with each other.
For example, JP-A-2006-193136 describes an example in which the malfunction diagnosis is performed using a plurality of such pressure sensors. The constitution shown in FIG. 1 of JP-A-2006-193136 is explained hereinafter.
A braking circuit 1a on a front-wheel side includes a master cylinder 3 which is interlockingly operated with a braking operation part 2 which constitutes a braking lever, a braking caliper 4 which is operated due to liquid pressure generated in the master cylinder 3, a main braking passage 5 which connects the master cylinder 3 and the braking caliper 4 respectively, and a first solenoid-operated open/close valve V1 provided to the main braking passage 5. Here, using the first solenoid-operated open/close valve V1 as a border, a first pressure sensor 28A and a second pressure sensor 28B are arranged on a braking input side which constitutes a master-cylinder-3 side, while using the first solenoid-operated open/close valve V1 as the border, a pressure sensor 29 is arranged on a braking output side which constitutes a braking caliper-4 side.
As described above, by arranging two pressure sensors, that is, the first pressure sensor 28A and the second pressure sensor 28B on the braking input side, it is possible to surely perform the malfunction diagnosis of these two sensors by comparing the detection values of the first pressure sensor 28A and the second pressure sensor 28B.
Further, a general liquid-pressure detection sensor used in these days is configured such that a pressure change is converted into a strain amount and an electric signal corresponding to the strain amount is outputted. Accordingly, when the liquid-pressure detection sensor is of a type which can detect a fine pressure change immediately after starting braking, the pressure resistance property against a high pressure tends to be lowered. On the other hand, when the liquid-pressure detection sensor is of a type which possesses high pressure resistance property against high pressure, the resolution for measuring a fine pressure change is lowered.